The present invention relates to a pipe socket seal for concrete pipes, of the type including a sealing ring of elastomer material fastened to the socket and a band-shaped fastening member cemented into the socket with the aid of a holding member. The fastening member includes a thickened sealing portion whose thickness corresponds to the intended compression of the sealing portion between the inner wall of the socket and the outer wall of the inserted pipe end. The sealing portion is moved from its installation state, or position, into an installed state, or position, by bending it over in the direction toward the bottom of the socket. Then, upon insertion of a pipe end into the socket, the sealing portion assumes an operating state.
The term "installation state" refers to the position of the sealing member with respect to the socket during manufacture and possibly during subsequent transport and storage. The term "operating state" refers to the position taken up by the sealing member when, during construction of a pipeline, the end of an adjacent pipe has been inserted into such a socket.
DE-OS [FRG Laid Open Application] No. 2,252,089 discloses a sealing arrangement for concrete pipes of the above-mentioned type. The prior art sealing arrangement is designed in the manner of a rolling ring seal. It differs, however, from the classical rolling ring seal in that it is cemented into the socket of the concrete pipe via a holding collar. In order for the sealing ring to be moved from its installation position into the sealing position or into the above-defined "operating state", when the tip end is pushed into the socket, it is necessary for the sealing ring to project in its cross section at least partially beyond the inner wall surface of the socket to assure that, when the tip end is inserted into the socket, the rolling process can take place.
With respect to manufacturing considerations, this sealing arrangement has the drawback that not only is it necessary to obtain specially shaped subsockets, or mold forms, for the manufacturing process, i.e. the previously customary subsockets can no longer be employed, but, in addition, due to the undercut position of the rolling region required in manufacture, an additional releasable shaping ring must be inserted into the socket. This makes the manufacturing process more difficult and expensive.
A certain drawback of the prior art seal is, moreover, that due to the rolling of the sealing member into its end position during insertion of the tip end, the sealing member comes to lie almost at the rear end of the socket so that the inserted tip end, after installation of the pipe, must be pressed practically in every case flush against the bottom of the socket in order to assure that the sealing ring is positioned properly.
A further drawback of the prior art seal is that during insertion of the tip end, the sealing ring is rolled over the part whose cross section is weakened because of the holding member that is cemented in at that point. Since, during the rolling process, practically the full compression of the sealing ring is already in effect, there exists the danger that the socket will burst apart at this point.
U.S. Pat. No. 3,866,925 discloses, particularly with respect to the embodiments shown in FIGS. 6, 12, 14, sealing arrangements which are fastened to a pipe socket via a portion embedded in the socket and in which the sealing element is formed by an annular lip which slides on the inserted pipe end when the latter is inserted. The sealing force is generated by a spring element which is embedded in the elastic material of the sealing lip.
One drawback of this prior art design is that the sealing force is predetermined by the spring element and is therefore reduced compared to sealing arrangements in which the sealing force is generated by compressing one sealing member. Since the sealing member has a lip-shaped design, there further results a linear-type contact with the counterface of the gap to be sealed so that here again, in conjunction with the reduced sealing forces, for example on rough concrete surfaces, the danger of leaks in the socket seal cannot be excluded.
The embodiment shown in FIG. 6 of U.S. Pat. No. 3,866,925 has the drawback that during insertion of the pipe end the free edge of the sealing element may be pulled into the inner end of the socket which is formed in order to protect the sealing element from shear loads and this may either damage the seal, particularly in its edge regions, or insertion of the pipe end beyond the end of that cavity is prevented completely so that the sealing element itself would have to absorb all transverse forces including traffic loads.
In the embodiment shown in FIG. 12 of U.S. Pat. No. 3,866,925, proper positioning of the sealing element on a smooth mold form, or subsocket, is impossible so that, on the one hand, auxiliary abutments must be used when the sealing element is pulled over the subsocket and these auxiliary abutments must be removed before the cementing process and, on the other hand, there exists the danger, during pouring of the cement, that the sealing element is displaced. In the embodiment shown in FIG. 14 of that patent, the undercut between the seal and the bottom of the socket again requires the additional provision of a removable shaping ring which must be applied to the subsocket before the cementing process.